Re: [Xen-devel] [PATCH] xen/vcpu: Sanitise VCPUOP_initialise call hierachy

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.10.2019 20:28, Andrew Cooper wrote:
> This code is especially tangled.  VCPUOP_initialise calls into
> arch_initialise_vcpu() which calls back into default_initialise_vcpu() which
> is common code.
> 
> This path is actually dead code on ARM, because VCPUOP_initialise is filtered
> out by do_arm_vcpu_op().
> 
> The only valid way to start a secondary CPU on ARM is via the PSCI interface.
> The same could in principle be said about INIT-SIPI-SIPI for x86 HVM, if HVM
> guests hadn't already interited a paravirt way of starting CPUs.
> 
> Either way, it is quite likely that no future architectures implemented in Xen
> are going to want to use a PV interface, as some standardised (v)CPU bringup
> mechanism will already exist.
> 
> Arrange the code in do_vcpu_op() to allow arch_initialise_vcpu() to be
> optional.  Opt in for x86, and opt out for ARM.
> 
> Deleting ARM's arch_initialise_vcpu() allows for default_initialise_vcpu() to
> be folded into its (now) sole x86 caller, which reduces the compiled code
> volume in all builds.
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

I can see the merits of this, but I can also understand Julien's
reservations. Hence I guess whether to ack this will depend on the
discussion with him getting settled.

Jan

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